The long-term objective of this project is to characterize the different structural variants and fragments of murine growth hormone (GH) in the pituitary gland and plasma of rats and mice. The hypothesis we want to test is that GH exists in several molecular forms and that the differences seen in its actions or biological and immunological activities are mostly a consequence of this molecular heterogeneity. Recent developments in the fields of GH purification and cloning of GH gene predict the existence of such variants. One specific aim is to identify the so-called 20,000-dalton (20K) variant, or a similar polypeptide, of GH in the murine pituitary gland. Our goal is to purify this protein from rat and mouse pituitary tissue, develop a radioimmunoassay for it and determine whether it circulates in blood. This polypeptide in humans is identical to the 22,000-dalton GH except that a 15 amino acid chain (residues 32 through 46) is missing from the NH2-terminal region. A second aim of this project is to develop a radioimmunoassay for this deletion peptide of murine species and determine whether it is present in circulation. A third aim is to determine the biologic and metabolic action of the murine 20K-GH and the 15-amino acid deleted fragment in order to determine structure-function relationships. The human deletion peptide potentiates insulin action in vitro and improves glucose tolerance in mice. A fourth aim of this project is to investigate the mechanism of action of a low MW hyperglycemic peptide of the human pituitary gland, which is dissociable from human GH. The peptide produces glucose intolerance in dogs and mice by interfering with insulin-stimulated glucose utilization. One and two-dimensional electrophoresis in basic and SDS gels and peptide mapping with HPLC will be used to identify the 20K-GH. Isolation will be carried out by chromatography on Sephadex and DEAE-cellulose. Radioimmunoassay will be developed by standard procedures. The study will help in understanding GH-related disorders.